The present invention is related to networking and more particularly to techniques for determining an optimized path for a local repair connection that is used to protect a connection in a network environment.
Connection-oriented protocols are widely used to transport data across computer networks. In a connection-oriented protocol, a connection is set up between two endpoints in a network, usually prior to data transmission. Network devices at the end points of a connection use a preliminary protocol to establish an end-to-end path traversed by the connection before any data is sent. The preconfigured connection with its associated path is then used to transport data between the end points. Examples of connection-oriented mechanisms include circuit switching protocols such as Asynchronous Transfer Mode (ATM) protocol, frame relay, Multi-Protocol Label Switching (MPLS), and others.
Multi-Protocol Label Switching (MPLS) (also referred to as “tag switching” or “label switching” protocol) is a data-carrying mechanism which emulates some properties of a circuit-switched network over a packet-switched network. It was designed to provide a unified data-carrying service for both circuit-based clients and packet-switching clients which provide a datagram service model. It can be used to carry many different kinds of traffic, including IP packets, as well as native ATM, SONET, and Ethernet frames.
MPLS works by prepending packets with an MPLS header, containing one or more “labels”. Switching nodes switch MPLS labeled packets after a Label Lookup/Switch instead of a lookup into the IP routing table. In MPLS, a connection between two end points is referred to as a Label Switched Path (LSP). Signaling protocol such as Label Distribution Protocol (LDP), Resource Reservation Protocol—Traffic Engine (RSVP-TE), Constrain-based Routed LDP (CR-LDP) and others may be used to set up an LSP. Routers in an MPLS LSP are referred to as Label Switching Routers (LSRs). The first router in an LSP is referred to as an ingress router and the last router in an LSP is referred to an egress router. Routers in between the ingress router and the egress router are referred to as transit routers. Forwarding of packets through an LSP is opaque to higher network layers and accordingly an LSP is also sometimes referred to as an MPLS tunnel. LSPs are unidirectional and enable a packet to be label switched through the MPLS network from one endpoint to another.
The ingress router for an LSP is configured to prepend an MPLS header to an incoming packet. The MPLS header comprises a label prepended based upon the appropriate forward equivalence class (FEC) of the packet. The packet with the MPLS header is then forwarded by the ingress router to the next router in the LSP path. The LSRs in the LSP make routing decisions for the packet based upon the label in the MPLS header. LSRs may swap the packet's outer label for another label. In this manner, the packet is label-switched by routers along the LSP. The egress router removes the MPLS header prior to forwarding the packet. In some embodiments, the last label may be popped off by the penultimate router (i.e., the LSR before the egress router).
A connection, such as an LSP in an MPLS network, established using a connection-oriented protocol may be affected due to failure of one or more nodes and/or links in the path traversed by the connection. As a result of such failures, the data transmission along the connection is prone to disruptions. To safeguard against such disruptions along the original preconfigured connection, one or more alternate connections are generally computed to bypass the network failure points along the original connection path. These connections are referred to as “local repair connections”. Each local repair connection originates at a start node in the original connection and ends at a node in the original connection that is downstream from the start node. A local repair connection enables data traffic to be rerouted or diverted around a network failure point in the original connection.
Different protocols may use different techniques to set up and maintain local repair connections. For example, RFC 4090 describes techniques to establish backup label-switched paths (LSP) tunnels for local repair of LSP tunnels. These mechanisms enable the redirection of traffic onto a backup LSP tunnel in the event of a failure. RFC 4090 describes two techniques for setting up local repair connections for an MPLS network—a “one-to-one backup” method that creates local repair LSPs for each protected LSP at each potential point of local repair and a “facility backup” method that creates a bypass tunnel to protect a potential failure point; the bypass tunnel can protect a set of LSPs that have similar backup constraints.
The local repair connections may be set up in advance or may be dynamically created as new LSPs are signaled. In embodiments, where the traffic needs to be redirected onto a backup or detour tunnel within a specified time limit (e.g., for voice over IP applications), the computing and signaling for the local repair connections is typically done in advance of the failure and the traffic is redirected onto the local repair connection as close to the failure point as possible.
A connection is said to be protected if at least one local repair connection has been set up for that connection. A node or link in a connection is said to be protected if at least one local repair connection has been configured that does not use that node or link. A connection is said to be protected at a given hop if it has one or multiple associated local repair LSPs (which may be detour LSPs or backup LSPs) originating at that hop.
Conventional techniques for creating local repair connections are however limited and inefficient, especially in the manner in which the paths associated with local repair connections are determined. Consequently, improved local repair connection techniques are desired.